An electronic device that receives radio signals such as television broadcast signals needs an antenna that receives radio signals. Since an electronic device, such as a mobile telephone terminal, is made compact for carrying purposes, its internal space into which an antenna is built is limited, so an antenna may be attached to the outside of the device.
In an example of an antenna attached to the outside of an electronic device, the antenna being in practical used, an earphone cable is used as an antenna element. When an earphone cable is used as an antenna element, an antenna is obtained that has a length needed to receive signals in the UHF band, in which television broadcast signals, for example, are transmitted, and the like.
PTL 1 describes a technology by which an antenna wire with a length suitable to a band, such as the UHF band, to be received is obtained by using only part of audio signal lines, which form an earphone cable, as the antenna element. That is, a high-frequency choke, which becomes a low impedance in a frequency band for voice signals and becomes a high impedance in a frequency band for reception signals, is connected at an intermediate point on the audio signal line. With the audio signal line with a high-signal choke connected as described above, a length used as the antenna element is determined depending on the location at which the high-signal choke is connected. Accordingly, an antenna element suitable to a band, such as the UHF band, to be received is obtained.